Stereo system



Sept. 19, 1961 E. H. UECKE ETAL STEREO SYSTEM Filed Oct. 26. 1959 INVENTORS M A/ES'SEL owl/r441 QTTQP/VEZ S FDW/OQD A! 056795 BY Z.

United States Patent 3,001,019 STEREO SYSTEM Edward H. Ueclre and Jiri M. Nessel, Los Angeles, Calif., assignors to Capitol Records, Inc., Los Angeles, Calif., a corporation of California Filed Oct. 26, 1959, Ser. No. 848,741 2 Claims. (Cl. 179-1) The present invention relates to an improved stereo system.

The conventional stereo amplifier consists essentially of two separate monaural amplifiers and a stereo pickup used to reproduce the so-called left and right channel recordings has its output coupled to such separate amplifiers.

In a stereo system, the input signals in the left and right channels are not necessarily equal and the above arrangement using two separate amplifying channels has the disadvantage that when a signal occurs in one channel only, no use is being made of the power available in the second channel so that the maximum output available in this particular case is reduced to 50% of total available output.

In accordance with the present invention a stereo amplifying system is provided in which the signals derived from a so-called left and right channel recording are amplified by the same amplifying tubes or transistors when the amplifier is transistorized, this being true regardless of whether the signal is derived from either the left or right channel or from both channels simultaneously, and thus the full power of the output tubes is at all times available for each channel. Using this circuitry, there is obviously an economy in both circuit components, their assembly and operating power.

An object of the present invention is to provide an improved stereo system involving novel connections of output transformers such that one of the transformers, acting as a push-pull type transformer, combines out-ofphase signals for operating its corresponding speaker and the same output transform-er serves effectively to cancel from such speaker in-phase signals corresponding to the other channel, there being provided a second transformer and a second speaker for combining the in-phase signals of such other channel and rejecting out-of-phase signals of such one channel.

Another object of the present invention is to provide an improved stereo amplifier of this character in which less distortion and higher efiiciency results.

Another object of the present invention is to provide a stereo amplifier of this character in which signals derived from the left and right channels are amplified in common amplifying tubes or transistors with means for separating the signals from the left and right channels prior to application to corresponding speakers.

Another object of the present invention is to provide an improved stereo system of this character which facilitates balancing of reproductions irom left and right channel recordings.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawings in which:

The single figure in the drawings illustrates a stereo amplifier embodying features of the present invention.

The amplifier presently described is particularly useful in the reproduction of stereo recordings from records or tapes and involves the use of two separate transducers and 11 for converting mechanical movement into Patented Sept. 19, 1961 corresponding electrical Variations, such mechanical movements or vibrations being produced by mechanical grooves in a record or in some cases by sound vibrations which may be used in effecting a recording either on a record or on a magnetizable tape. Also, in some cases the transducers 10 and 11 may comprise coils for inducing voltage corresponding to recordings on magnetized tape.

A stereo system of this type may, for purposes of definition, be considered to include a so-called left channel recording or signal and a so-called right channel recording or signal, the transducer 10 in this instance serving as the pickup means for the left channel signal and the transducer 11 serving as the pickup transducer for the right channel signal.

The transducer 10 has one of its terminals coupled through the parallel connected resistance 12 and condenser 14 to one terminal of the potentiometer-type volume control resistance 15, the other terminal of transducer 10 being similarly connected in balanced relationship through the parallel connected resistance 16 and condenser 18 to one terminal of the otherpotentiometertype volume resistance 17. The other terminals of resistances 15 and 17 are both connected to a grounded B-m-inus terminal or, in this case when the amplifier is supplied with power from an A.C.-DC. type rectifier source, the same is connected to the so-called B-minus terminal 19 which is not conductively connected to the chassis on which the components are mounted. The term B-minus terminal has reference to the minus terminal of the energizing voltage source.

The taps 15A and 17A of resistances l5 and 17 are ganged as indicated by the dotted line 20 for simultaneous movement by a suitable volume control knob (not shown). These taps are so ganged that they may be either moved closer together or farther apart simultaneously.

The right channel transducer 11 has one of its ter minals connected to the B-minus terminal 19 through condenser 21, the other terminal of transducer 11 being connected through the parallel connected resistance 23 and condenser 25 to the upper terminal of resistance 15; and similarly, such other terminal of transducer 11 is connected to the lower terminal of resistance 17 through the parallel connected resistance 27 and condenser 29.

When using an A.C.-DC. power supply as described herein, the B-minus terminal 19 is connected to the metal chassis 30 on which the circuit components shown herein are mounted through condenser 32. When an A.C. power supply is used, i.e. one in which an isolating transformer is incorporated, the B-minus terminal may be connected conductively to the chassis instead of through a condenser as shown.

The taps 15A and 17A are coupled through corresponding coupling condensers 33 and 34 to corresponding grids 35 and 36 of tubes 37 and 38, these grids 35, 36 being returned to the B-minus terminal 19 through corresponding resistances 39 and 40 to provide bias for the control grids of these tubes 37 and 38. It is noted that the cathodes of these tubes 37, 38 are connected to the B-minus terminal 19.

The anodes of tubes 37 and 38 are coupled by means of corresponding condensers 39 and 40 to the control grids 41 and 42 of corresponding tubes 43 and 44, each having their cathodes 45 and 46 respectively returned to the B-minus terminal 19 through the parallel connected resistance 47 and the condenser 48 which serve to provide the bias for tubes 43 and 44. The control grids 41 and 42 are returned to the B-minus terminal 19 through corresponding resistances 51 and 52. Space current for the anodes of tubes 37 and 38 is supplied from the 3 B-plus lead 53 through corresponding load resistances 55 and 56.

A tone control circuit is connected in the input circuit of tubes 43 and 44 and such tone control circuit comprises the condenser 57, adjustable resistance 59, adjustable resistance 58 and condenser 60. The junction point of resistances 58 and 59 is connected to the B-minus terminal 19. The adjustable tap 59A on resistance 59 is connected through condenser 57 to the control grid 41; and similarly, the tap 58A on resistance 58 is connected to the control grid 4-2 through condenser 60. These taps 58A and 5 1A are ganged for simultaneous movement by a control knob (not shown) but, as indicated by the dotted line 62, such that these taps 58A and 59A may be simultaneously moved closer together or farther apart, depend ing upon the tone desired.

The tubes 43 and 44 may be of the screen grid type as shown or may be of the pentode type and, indeed, may be included in the same envelope as are the elements of tubes 37 and 38, i.e. in a dual purpose tube. In such case 4 the tubes 37 and 43 may be designated as a single tube V and the tubes 38 and 44 may be designated as a single tube V The screen grids 63 and 64 of tubes 43 and 44 may be, as illustrated, connected directly to the B-plus lead 53.

In accordance with an important feature of the present invention as will be described in more detail later, the anodes 65 and 66 of tubes 43 and 44 respectively are connected in a novel manner with respect to their corresponding output transformers 67 and 68, each of which has its corresponding secondary winding connected to a voice coil of speakers 69 and 70. The transformer 67 is of the so-called push-pull type having a center-tapped primary winding 67A for combining out-of-phase signals and for effectively cancelling in-phase signals; and the primary winding 68A of transformer 63 is untapped to combine in-phase signals and to effectively cancel outof-phase signals.

Space current to the anode 65 is supplied from the B plus lead 53A through a series circuit which includes the primary winding 68A, the tap 67B on primary winding 67A and the upper half of such primary winding 67A. Space currentfor the anode 66 is supplied from the same B-plus lead 53A through a series circuit which includes the primary winding 63A, the tap 67B and the lower half of the primary winding 67A.

As shown, a condenser 71 may interconnect the anode 65 to the screen grid 63; and similarly, a condenser 72 may interconnect the anode 66 and screen grid 64.

The amplifier circuit thus described may be powered from any suitable source and, as illustrated herein, the same is supplied from an A.C.-D.C. type power supply having its input terminals in the form of a conventional household plug 95 connectible to household mains.

One terminal 96 of the source represented by the power plug 95 is connected to the B-minus terminal 19, such terminal 19, as previously described, being connected through condenser 32 to the metal chassis 30. The other terminal 9'7 of the source is connected through the On- Olf switch 99 through the voltage dropping resistance 160 to the serially connected filaments F and P of tubes V and V Also, such terminal 97 is connected through the On-Off switch 99 to the serially connected resistance 161, silicon-type rectifier 102 and filter resistance 163, one terminal of resistance 163 being connected to the B-minus lead terminal 19 through condenser 10 and the other terminal of resistance 103 being connected to the B- minus terminal 19= through condenser 165 to provide a rectified and filtered B-plus voltage on lead 53A. It is noted that the other B-plus lead 53 is connected to the junction point of resistance 106 and condenser 107 which are serially connected in a shunt circuit with respect to condenser 105 to thereby provide a somewhat lower B- plus voltage on lead 53 than that which exists on lead 53A and condenser 107 serves as a filter element together with the voltage dropping resistance 106.

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in operation of the circuit described above, it is assumed that the values of resistances 12 and 16 are equal and that the values of resistances 23 and 27 are equal. Thus, the voltage developed across the terminals of trans ducer 10 from the left channel of the stereo recording appears across the resistances 23 and 27 with equal amplitude. The magnitude of this voltage is adjustable by the ganged volume control 15, 17. Condensers 33 and 34 couple this voltage to the grids 35 and 36, the bias for these grids being provided by resistances 39 and which may have, for example, a magnitude of 10 megohms. This voltage derived from the left channel appears in opposite phase on the grids 35 and 36; and correspondingly, the amplified voltages developed on the anodes of tubes 37 and 38 are of opposite phase. This left channel amplified voltage is coupled through condensers 39 and 419 to the control grids 41 and 42 of tubes 43 and 44, is amplified in the tubes 4-3 and 44 and again appears in opposite phase on the anodes and 66. These amplified voltages developed on the anodes 65 and 66, of equal magnitude but of opposite phase, are applied to the outside terminals of the primary winding 67A, and by conventional push-pull action these signals of opposite phase are combined in the secondary winding 67C connected to the coil of speaker 69. Thus, the speaker 69 reproduces the signals derived from the left channel by transducer 11). It is noted that the full power of both output tubes '43 and 44 may be utilized for this purpose. It is noted that the space current for the anodes 65 and 66 flows also through the primary winding 63A of the transformer 68 but since the amplified signal voltages developed on the anodes 65 and 66 are out of phase, the net voltage developed in the secondary winding of transformer 63A, due to signals developed in the left channel, is substantially and effectively canceled out, i.e. has substantially no effect on the coil of speaker 76 in the right channel.

An electrical signal developed across the terminals of the right channel transducer 11 is applied through resistances 23 and 27 and the same ganged volume control 15, 17 and the same coupling condensers 33 and 34 to the control grids 35' and 36; and it will be observed that in this instance the voltages thus developed on the control grids 35 and 36 are not out of phase as is the case with t. e left channel signal but are in phase. Thus, in-phase amplified signals of equal magnitude are developed on the anodes of tubes 37, 38 and such voltages are further amplified in tubes 43 and '44 and again appear as in phase equal amplitude signals on the anodes 65 and 66. These in-phase signals are combined in transformer 68 with the speaker 70, thus reproducing the amplified right channel signal orginally developed in the right channel transducer 11. It is noted that the space current for tubes 43 and 44 also passes through different halves of the primary winding 67A but the in-phase signals developed on the anodes 65 and 66 are effectively canceled out by the push-pull type transformer 67 so that substantially no right channel signal is reproduced by the speaker 69. Here again, the output tubes 43 and 44 may be using the full available power in reproducing the signal in the right channel while the signal in the left channel may be substantially zero or of little value.

When both right and left channels operate at the same time, the full power of both tubes is made available for variable peak; voltages in the right and/or left channel or may be used in proportion whenever the need may arise. Less distortion, economy and higher efficiency is the result of this combination.

It is noted that the sum of the values of resistances 12, 23, 27 and 16, and the value of the ganged volume control 15 and '17 which is connected in parallel with resistances 23 and 27;, constitutes the load for the transr ducer '10; and that the resistances 23, 27 and the ganged resistances 15 and 17' constitute the load for the other transducer 1 1. The ratio between the values of the resistances 12 and 23 and between 1-6 and 27 determines the ratio of the magnitude of signals reaching speakers 69 and 70.

The condensers 14, 25, 2 and 18 are included in the circuit to modify the frequency responses in the left and right channels to compensate for deficiencies which may appear in output transformers 67 and 68 and corresponding speakers 69 and 70. In some cases these condensers 14, 25, 29 and 18 may be omitted when precise balance between left and right channels is not required.

The condensers 57 and 60 in combination with the ganged potentiometer-type resistances 5'8 and 59 provide a tone control by diminishing the high frequency response. The condensers 71 and 72 may be used for stability and for attenuating high order harmonics.

Other tone controls and balance controls may be added in any suitable way. A negative feedback loop may be incorporated to reduce distortion. Such feedback loop may be operated in either the left channel or right channel or in both channels.

While the particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

We claim:

1. In a stereophonic system, an amplifying channel comprising a pair of amplifying devices, each of which includes a control element, said channel having three input terminals, one of which is a common terminal and the other two of which comprise respectively said control element of a corresponding one of said devices, a first transducer for producing a first signal, said first transducer having one of its terminals coupled to said common terminal and the other one of its terminals coupled to said control element of each of said devices to produce in-phase components of said first signal on said control elements, a second transducer for producing a second signal, said second transducer having a corresponding one of its two terminals coupled respectively to a corresponding one of said control elements to produce thereon outof-phase components of said second signal, each of said devices having an output element, said amplifying channel comprising a three-terminal output circuit of which two terminals are coupled respectively to the output element of each device and the third terminal is common to each output element, means coupled to said three-terminal output circuit for reproducing amplified in-phase components of said first signal on said output elements and for producing amplified out-of-phase components of said second signal on said output elements, the last-mentioned means comprising: a first center tapped winding and a second winding, the outside terminals of said first winding being coupled to corresponding ones of said output elements, the second winding having one of its terminals coupled to the center tap on said first winding and the other one of its terminals coupled to said third terminal, first signal reproducing means coupled to said first winding, and second signal reproducing means coupled to said second winding, said terminals of said second transducer being coupled to corresponding control elements through corresponding resistances of equal values, and each of said resistances being shunted by a corresponding condenser of equal values.

2. In a stereophonic system, an amplifying channel comprising a pair of amplifying devices, each of which includes a control element, said channel having three input terminals, one of which is a common terminal and the other two of which comprise respectively said control element of a corresponding one of said devices, a first transducer for producing a first signal, said first transducer having one of its terminals coupled to said common terminal and the other one of its terminals coupled to said control element of each of said devices to produce in-phase components of said first signal on said control elements, a second transducer for producing a second signal, said second transducer having a corresponding one of its two terminals coupled respectively to a corresponding one of said control elements to produce thereon outof-phase components of said second signal, each of said devices having an output element, said amplifying channel comprising a three-terminal output circuit of which two terminals are coupled respectively to the output element of each device and the third terminal is common to each output element, means coupled to said threeterminal output circuit for reproducing amplified in-phase components of said first signal on said output elements and for producing amplified out-of-phase components of said second signal on said output elements, the lastmentioned means comprising: a first center tapped winding and a second winding, the outside terminals of said first winding being coupled to corresponding ones of said output elements, the second winding having one of its terminals coupled to the center tap on said first winding and the other one of its terminals coupled to said third terminal, first signal reproducing means coupled to said first winding, and second signal reproducing means coupled to said second winding, said other terminal of said first transducer being coupled to each of said control elements through corresponding resistances of equal values, and each of said resistances being shunted by corresponding condensers of equal values.

References Cited in the file of this patent 2-Way Stereo Amplifier, Radio-Electronics, December 1958 (pp. 41, 42 relied upon). 

